An Earth Leakage Circuit Breaker was the first name given to what is now called a Ground Fault CircuitInterrupter (GFCI) . The original type of ELCB or GFCI was designed only to detect a current flowing in the safety “ground” or “earth” wire.
If there is no fault anywhere in a circuit supplying single-phase alternating power to a unit such as an electrical appliance, machine or other equipment, the current flowing to the unit at any instant in the “hot” or “live” wire should exactly match the current flowing away from the unit in the neutral wire. Similarly, there should be no current flowing in the unit’s safety “ground” or “earth” wire.
It is a basic fact of electrical engineering design that all current flowing to an electrical appliance, machine or other equipment from the power generation station via its supply circuit’s “hot” or “live” wire should only return to the power station via that same circuit’s “neutral” wire.
So, as a result of that basic fact, if any current is flowing in the ground wire, it must be caused by a fault condition and the supply of current to the circuit needs to be stopped urgently. Many years ago, before today’s electronic RCDs or GFCIs were designed, much simpler electro-mechanical relays called EarthLeakage Circuit Breakers (ELCBs) were invented so that, if any such ground current exceeding just a few milliamps was detected, they would “trip” - meaning “operate” - to break the current supply to the circuits for which they were installed to protect.
The original type of ELCB or GFCI did not check for any difference in current flowing in the live and neutral wires, which is another indication of a very serious fault condition - even if no current can be detected flowing in the ground wire - because the “missing current” may actually be flowing to ground via someone’s body!
When RCDs were invented, most manufacturers of GFCIs adopted the same technology because it offers so much more protection to users than the original GFCI could ever give. In the US and Canada such devices are still commonly known as “GFCIs” or “GFIs” even though they have the additional “residual current detector” functionality, whilst in Europe and elsewhere the more accurate name of “Residual Current Detector” or RCD has been widely adopted for general use instead of using the name of the much simpler GFCI device.
Nowadays we use more commonly miniature circuit breaker or MCB in low voltage electrical network instead of fuse. The MCB has some advantages compared to fuse.
It automatically switches off the electrical circuit during abnormal condition of the network means in over load condition as well as faulty condition. The fuse does not sense but miniature circuit breaker does it in more reliable way. MCB is much more sensitive to over current than fuse.
Another advantage is, as the switch operating knob comes at its off position during tripping, the faulty zone of the electrical circuit can easily be identified. But in case of fuse, fuse wire should be checked by opening fuse grip or cutout from fuse base, for confirming the blow of fuse wire.
Quick restoration of supply can not be possible in case of fuse as because fuses have to be rewirable or replaced for restoring the supply. But in the case of MCB, quick restoration is possible by just switching on operation.
Handling MCB is more electrically safe than fuse. Because of to many advantages of MCB over fuse units, in modern low voltage electrical network, miniature circuit breaker is mostly used instead of backdated fuse unit.